1. Field of the Invention
The present invention relates to ultrashort pulse laser machining, and more specifically, it relates to techniques for machining layered materials and articles without affecting other than the first layer.
2. Description of Related Art
In many materials processing applications it is important to penetrate the work item frontal piece using some form of energy, laser beams or electron beams being examples, without causing damage to subsequent surfaces facing the laser or electron beam. One example of this is the need to place holes in fuel injectors without damaging the back surface of the sack in which the fuel is combusted. Damage to this back surface severely reduces the reliability of the overall fuel injector as its subsequent exposure to extremely high temperatures and pressures requires that the fuel injector be of very high integrity.
The mechanical structure of fuel injectors (or other components requiring that portions of the piece be machined without causing damage to the remainder of the piece) usually severely limits the strategies for machining. In the case of fuel injectors the back or subsequent surface encountered by the machining laser or electron beam is typically only some millimeters away from the machined surface. Therefore, a laser beam that is of high enough intensity to cut or drill the frontal piece remains high enough in intensity at the subsequent surface to damage it. One strategy that has been tried is to insert a flowing, absorbent liquid between the frontal piece and the back surface (fill the "sack"). Unfortunately, the severe constriction of the sack region does not allow the liquid to be flowed fast enough to avoid bleaching of the dye by high energy pulses from high repetition rate machining lasers. Another strategy has been to plug the sack region with a non-flowing absorbent solid. However, the energy absorbed by the absorbing solid is so great that it in turn heats up and damages the surrounding surfaces in the sack.